 Today, we're going to start deviating a little bit from all the theory and paper and pen and look more at computer simulations. This is important for a couple of reasons. First, it will be the first step where we can move to more realistic systems. It will enable you to, in the labs, use computer simulations to test things on real proteins and make sure that I didn't lie to you. Second, there has been a dramatic development the last decade or so where we are increasingly using computer simulations for all sorts of applications in biochemistry and life sciences. In fact, today, if you're publishing a high-impact structure of a new protein or iron channel or something, it can't even be difficult to get it published unless you also have a computer simulation showing something of a mechanism. And the third part is that it's a fairly beautiful connection, I think, between the paper and pen simple theory and taking that over to much more complex systems that they still treat correctly in terms of statistical mechanics, including all states, and bridging that to the very high-level simplified macroscopic systems that we're increasingly going to talk about from the life science side. So, join me. Proteins. You should know all about proteins by now, at least the secondary structures, in terms of entropy, enthalpy, and free energy, right? You can probably reason about the free energy of the secondary structure elements here, and yet there's this problem that the entropy here is zero, because this is just one microstate. You don't have an ensemble of many states here, and it's not moving, and if it's one microstate, the logarithm of that is zero, so the entropy is zero, just as it was zero Kelvin. What I really would like to get at is this. You see that it's a beautiful protein moving, the secondary structure elements might be breathing a little bit or whatever you call it. The side chains here are jumping a little bit back and forth, rotating around their torsions. There might be some waters jumping in and out. You have to trust me that there is water here. I've just removed it so that to make the protein more visible, and there might even be some side chains here that are changing some of the chi torsions a little bit. It's stable, it's not really moving away, and yet it's definitely not a crystal. It's much more flexible and full of motion than a pure crystal. Computer simulations will allow us to treat this, and there turns out there are two ways we can introduce them. One that is obvious, and the other one I would argue is more correct, so I'm going to take you through both.